The present invention relates to a method for operating an electrical system, in particular of a motor vehicle, wherein the electrical system has at least one electrical energy store, in particular an electrical high-voltage energy store, and at least two electrical machines which are connected to the electrical system by means of a controllable inverter in each case, wherein a regulated generator mode of a first of the electrical machines is initiated for supplying electrical energy to the system.
The present invention also relates to an apparatus for controlling an electrical system, in particular of a motor vehicle, comprising voltage detection means for detecting an available voltage in the system, and a control unit which is designed to execute the above-described method.
Finally, the present invention relates to an electrical system, in particular for a motor vehicle, comprising an electrical energy store, in particular an electrical high-voltage energy store, and at least two electrical machines which are connected to the electrical system by means of a controllable inverter in each case, and comprising a control unit of the above-mentioned type.
In order to operate an electrical network in a hybrid motor vehicle, it is known, when detecting a malfunction of an electrical energy store, to electrically disconnect said electrical energy store from the network and to switch the electrical machine of the hybrid motor vehicle to a freewheeling mode in order to provide the network with a freewheeling voltage which is induced by the rotating electrical machine, which is mechanically driven by means of the drive train, and is used to reactivate the voltage regulation means. In this case, the freewheeling mode is initiated by opening the circuit breaker of the inverter and providing the network with the freewheeling voltage which is induced by the electrical machine with permanent-magnet excitation.
A method of this kind is known, for example, from WO 2009/083342.
The induced freewheeling voltage of an electrical machine is dependent on the rotation speed of the electrical machine. At very high rotation speeds or very low rotation speeds of the electrical machine, it is possible for the induced freewheeling voltage to be outside a permissible range. If the voltage is too low, the voltage in the network cannot be regulated. If the voltage is too high, components may be damaged by overvoltages.